Various fluid heating systems utilizing, for example, hot water, have been used to provide radiant heat to selected spaces. In my copending U.S. patent application Ser. No. 931,682, filed November 17, 1986, there is described a heating system involving a plurality of tubes that are imbedded in a floor and to which water at a preselected temperature is provided by means of a fluid flow control apparatus which includes a pump. It was contemplated that several of the flow control units would be employed in a single building to control the temperature of various floor areas.